Wireless communication device

ABSTRACT

A wireless communication device includes a wireless IC chip that processes a high-frequency signal and a feeding substrate including a coil conductor, a plane conductor, and a matching circuit that is connected to the wireless IC chip and that has a predetermined resonant frequency. The coil conductor and the plane conductor are connected to the matching circuit. The wireless communication device, when used by itself, operates as a monopole antenna in which the plane conductor functions as a ground and the coil conductor functions as a radiation element. When a conductive object is in a vicinity of the plane conductor, the plane conductor is coupled to the conductive object, and the wireless communication device operates as a dipole antenna in which the plane conductor and the conductive object function as a first radiation element and the coil conductor functions as a second radiation element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication devices, andspecifically to wireless communication devices that communicate withreaders/writers in radio frequency identification (RFID) systems.

2. Description of the Related Art

Known article management systems include an RFID system in which areader/writer communicates with RFID tags (also called wireless ICdevices) in a noncontact manner, whereby information is transmittedbetween the reader/writer and the RFID tags. An RFID tag includes awireless IC chip for processing wireless signals and an antenna fortransmitting/receiving wireless signals, and predetermined informationis transmitted/received as high-frequency signals between the antenna ofan RFID tag and the antenna of a reader/writer via a magnetic field oran electric field.

Generally, dipole antennas are used as antennas of RFID tags, asdescribed in Japanese Unexamined Patent Application Publication No.2004-104344, Japanese Unexamined Patent Application Publication No.2009-524363, and International Publication No. 2007/013168. A dipoleantenna, which transmits/receives signals mainly using an electricfield, has a long communication range when used by itself. However, whenan object with a large relative dielectric constant or a largeelectroconductivity is in the vicinity of the antenna, the radiationcharacteristics are likely to change.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a wirelesscommunication device that has stable communication characteristics thatare not particularly dependent on the surrounding environment.

A wireless communication device according to a preferred embodiment ofthe present invention includes a wireless IC chip that processes ahigh-frequency signal, and a feeding substrate including a coilconductor, a plane conductor, and a matching circuit that is connectedto the wireless IC chip and that has a predetermined resonant frequency,wherein the coil conductor and the plane conductor are connected to thematching circuit, the wireless communication device, when used byitself, operates as a monopole antenna in which the plane conductorfunctions as a ground and the coil conductor functions as a radiationelement, and when a conductive object is in a vicinity of the planeconductor, the plane conductor is coupled to the conductive object andthe wireless communication device operates as a dipole antenna in whichthe plane conductor and the conductive object function as a firstradiation element and the coil conductor functions as a second radiationelement.

The wireless communication device, when used by itself, behaves as amonopole antenna in which the plane conductor connected to the matchingcircuit that is coupled to the wireless IC chip functions as the groundand the coil conductor connected to the matching circuit functions as anantenna element, and the wireless communication device transmits andreceives high-frequency signals to and from the antenna of acommunication partner. On the other hand, when there is a nearbyconductive object such as a metal member, the plane conductor and theconductive object are coupled to each other, and the wirelesscommunication device behaves as a dipole antenna in which the planeconductor and the conductive object function as a first radiationelement and the coil conductor functions as a second radiation element,and the wireless communication device transmits and receiveshigh-frequency signals to and from the antenna of a communicationpartner.

The wireless communication device according to a preferred embodiment ofthe present invention behaves as a monopole antenna or a dipole antennain accordance with the existence/nonexistence of a nearby conductiveobject and, hence, exhibits stable communication characteristics thatare not particularly dependent on the surrounding environment.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a wireless communicationdevice according to a preferred embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the wireless communicationdevice.

FIG. 3 is an exploded perspective view of a feeding substrate of thewireless communication device.

FIGS. 4A-4C illustrate a first type of operation of the wirelesscommunication device, where FIG. 4A is a perspective view, FIG. 4B is anoperation explanation diagram, and FIG. 4C is an equivalent circuitdiagram for during operation.

FIGS. 5A-5C illustrate a second type of operation of the wirelesscommunication device, where FIG. 5A is a perspective view, FIG. 5B is anoperation explanation diagram, and FIG. 5C is an equivalent circuitdiagram for during operation.

FIG. 6 is a perspective view illustrating an example of mounting of thewireless communication device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of a wireless communication deviceaccording to the present invention will be described with reference tothe attached drawings. Note that identical components and portions inthe figures are denoted by the same reference symbols and duplicatedescriptions thereof are omitted.

Referring to FIG. 1, a wireless communication device 1 according to apreferred embodiment of the present invention, which is preferably usedin a UHF band RFID system, includes a wireless IC chip 50 functioning asa feeding circuit and a feeding substrate 10 that includes a matchingcircuit 20 having a predetermined resonant frequency and coupled to thewireless IC chip 50, a coil conductor 31, and a plane conductor 35. Thecoil conductor 31 and the plane conductor 35 are electrically connectedin parallel with the matching circuit 20. One end of the coil conductor31 is connected to a first connection point P1 of the matching circuit20 and the other end is open. The plane conductor 35 is provided on thebottom surface side of the feeding substrate 10 over a relatively widearea and is connected to a second connection point P2 of the matchingcircuit 20. Note that the matching circuit 20 is illustrated in asimplified manner in FIG. 1.

The wireless IC chip 50, which is mounted on the feeding substrate 10,has a function of processing high-frequency signals, and preferably is asilicon semiconductor integrated circuit chip, for example. The wirelessIC chip 50 includes a clock circuit, a logic circuit, a memory circuit,and the like, and stores necessary information. The wireless IC chip 50includes a pair of input/output terminals, which define balancedterminals.

Referring to FIG. 2, the matching circuit 20 includes inductanceelements L1 and L2 and capacitance elements C1 and C2. The inductanceelements L1 and L2 are electrically connected in parallel with thewireless IC chip 50. In other words, the matching circuit 20 is insertedbetween the pair of balanced terminals. The capacitance element C1 isconnected in series with the inductance element L1, thereby defining afirst series resonant circuit. The capacitance element C2 is connectedin series with the inductance element L2 so as to define a second seriesresonant circuit.

In other words, the matching circuit 20 has a predetermined resonantfrequency that is determined by the first and second series resonantcircuits. The plane conductor 35 is connected to the capacitance elementC1 of the first series resonant circuit, and the coil conductor 31 isconnected to the capacitance element C2 of the second series resonantcircuit. The inductance elements L1 and L2 respectively include windingswound in opposite directions so as to define a closed magnetic path, andthere is strong magnetic coupling M therebetween. An inductance elementL3 that adjusts the coupling value of the magnetic coupling M isinserted between the capacitance elements C1 and C2 that respectivelydefine portions of the first and second series resonant circuits.

Referring to FIG. 3, the feeding substrate 10 preferably is a multilayersubstrate which is preferably formed by stacking a plurality ofdielectric layers or magnetic layers. Connection electrodes 18 a to 18 dare provided on the top surface of a first layer 11 a, coil patterns 12a, 13 a, and 31 a are provided on the top surface of a second layer 11b, and coil patterns 12 b, 13 b, and 31 b are provided on the topsurface of a third layer 11 c. Further, capacitor patterns 14 a and 15 aand a coil pattern 31 c are provided on the top surface of a fourthlayer 11 d, and capacitor patterns 14 b and 15 b, a meandering pattern16, and a coil pattern 31 d are provided on the top surface of a fifthlayer 11 e. The plane conductor 35 is provided on the top surface of asixth layer 11 f.

Note that in the present preferred embodiment, the first layer 11 a tothe fifth layer 11 e are dielectric layers and only the sixth layer 11 fis a magnetic layer.

By stacking the layers 11 a to 11 f, the coil patterns 12 a and 12 b areconnected to each other through a via-hole conductor 17 b so as todefine the inductance element L1, and the coil patterns 13 a and 13 bare connected to each other through a via-hole conductor 17 e so as todefine the inductance element L2. The capacitor patterns 14 a and 14 bface each other, and the capacitor patterns 15 a and 15 b face eachother, so as to respectively define the capacitance elements C1 and C2.The coil patterns 31 a to 31 d are connected to one another in a spiralshape through via-hole conductors 32 a to 32 c so as to define themultilayer coil conductor 31.

The meandering pattern 16 defines the inductance element L3, and one endthereof is connected to the capacitor pattern 14 b and the other endthereof is connected to the capacitor pattern 15 b and an end of thecoil pattern 31 d. The connection electrode 18 a is connected to one endof the inductance element L1 (the coil pattern 12 a) through a via-holeconductor 17 a. The connection electrode 18 b is connected to one end ofthe inductance element L2 (the coil pattern 13 a) through a via-holeconductor 17 d. Further, the other end of the inductance element L1 (thecoil pattern 12 b) is connected to the capacitor pattern 14 a through avia-hole conductor 17 c. The other end of the inductance element L2 (thecoil pattern 13 b) is connected to the capacitor pattern 15 a through avia-hole conductor 17 f. Further, the capacitor pattern 14 b isconnected to the plane conductor 35 through a via-hole conductor 36.

Note that various ceramic materials can be used as the dielectric layersor magnetic layer defining the feeding substrate 10. Resin materialssuch as polyimide and liquid crystal polymers may be used. When thefeeding substrate 10 is formed of a ceramic material, the conductivepatterns provided on the layers are preferably formed using a conductivepaste mainly composed of a low-melting point material, such as silver orgold, for example, which has a low resistivity and can enhancehigh-frequency characteristics. When the feeding substrate 10 is formedof a resin material, the conductor patterns may be formed by etching ametal foil or metal film of, for example, silver or copper.

In other words, in the present preferred embodiment, the feedingsubstrate 10 is a multilayer substrate and the matching circuit 20 isprovided within the feeding substrate 10. However, it is not necessaryto dispose all the elements L1, L2, L3, C1, and C2 within the feedingsubstrate 10.

The wireless IC chip 50 includes a pair of input/output electrodes 51 aand 51 b (refer to FIG. 1) to receive a high-frequency signal as apotential difference. The input/output electrodes 51 a and 51 b areconnected to the connection electrodes 18 a and 18 b provided on thefeeding substrate 10 using, for example, solder bumps 52.

Referring to FIG. 4, the wireless communication device 1 is used in sucha manner as to be mounted on a printed circuit board 60. When aconductive object such as a ground plate or metal casing is not presentin the vicinity of the wireless communication device 1, the wirelesscommunication device 1 behaves as a monopole antenna in which the planeconductor 35 connected to the matching circuit 20 that is coupled to thewireless IC chip 50 functions as the ground and the coil conductor 31connected to the matching circuit 20 functions as a radiation element,and the wireless communication device 1 transmits and receiveshigh-frequency signals to and from the antenna of a reader/writer, whichis not illustrated, over a relatively short distance (for example, about10 cm or less) using an electromagnetic field (mainly magnetic field).

On the other hand, referring to FIG. 5, when a conductive object 61,such as a ground plate, is provided on the printed circuit board 60,that is, when the conductive object 61 such as a ground plate or a metalcasing is in the vicinity of the plane conductor 35, the wirelesscommunication device 1 behaves as a dipole antenna in which the planeconductor 35 and the conductive object 61, which are capacitivelycoupled to each other, function as a first radiation element and thecoil conductor 31 functions as a second radiation element, and thewireless communication device 1 transmits and receives high-frequencysignals to and from the antenna of a reader/writer, which is notillustrated, over a relatively long distance (for example, about 30 cmor more) using an electromagnetic field (mainly magnetic field).

In the above preferred embodiment, in describing the wirelesscommunication device 1, a non-limiting example of a manner in which thewireless communication device 1 is mounted on the printed circuit board60 has been described. Other than this, the wireless communicationdevice 1 may be mounted on various articles or the packages of thearticles. FIG. 6 illustrates a manner in which the wirelesscommunication device 1 is mounted on a package 70 of a food product. Thepackage 70 is a package with an evaporated aluminum film all over thesurface thereof, and the wireless communication device 1 is attached toa seam portion 71 which is the periphery of a conductive evaporatedaluminum film 72.

Note that the wireless communication device according to the presentinvention is not limited to the preferred embodiment described above,and various modifications are possible within the scope of the presentinvention.

In particular, the matching circuit can include various circuitelements, and is not limited to the circuit configuration which uses theinductance elements L1 and L2 and the capacitance elements C1 and C2illustrated in the preferred embodiment described above. Further, thecoupling between the matching circuit and the wireless IC chip may beany of magnetic coupling, capacitive coupling, electric field coupling,electromagnetic coupling, and direct current coupling. The couplingbetween the plane conductor 35 and the conductive object 61 may insteadbe any of magnetic coupling, electric field coupling, electromagneticcoupling, and direct current coupling, rather than capacitive coupling.

The wireless IC chip, rather than being mounted on the top surface ofthe feeding substrate, may be disposed within the feeding substrate(housed in a cavity formed in the feeding substrate) or may be mountedon a substrate other than the feeding substrate.

As described above, preferred embodiments of the present invention andmodifications thereof are useful in wireless communication devices, andspecifically provide an advantage in that stable communicationcharacteristics that are not particularly dependent on the surroundingenvironment are realized.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A wireless communication device comprising: awireless IC chip that processes a high-frequency signal; and a feedingsubstrate including a coil conductor, a plane conductor, and a matchingcircuit that is connected to the wireless IC chip and that has apredetermined resonant frequency; wherein the coil conductor and theplane conductor are connected to the matching circuit; and the wirelesscommunication device is configured such that when the feeding substrateis arranged to face a conductive object in a planar view, the conductiveobject overlaps the plane conductor and does not overlap the coilconductor.
 2. The wireless communication device according to claim 1,wherein the plane conductor is capacitively coupled to the conductiveobject.
 3. The wireless communication device according to claim 1,wherein the matching circuit includes a first inductance element and asecond inductance element, and the first and second inductance elementsare electrically connected in parallel with the wireless IC chip andmagnetically coupled to each other.
 4. The wireless communication deviceaccording to claim 1, wherein the feeding substrate includes amultilayer body including a plurality of dielectric layers or magneticlayers stacked on each other, and the matching circuit is located withinthe multilayer body.
 5. The wireless communication device according toclaim 1, wherein the coil conductor is a multilayer coil patternincluding a plurality of loop-shaped conductors stacked on and connectedto each other in a spiral shape.
 6. The wireless communication deviceaccording to claim 1, wherein the wireless IC chip is a siliconsemiconductor integrated circuit chip.
 7. The wireless communicationdevice according to claim 1, wherein the wireless IC chip includes aclock circuit, a logic circuit, and a memory circuit.
 8. The wirelesscommunication device according to claim 1, wherein the wireless IC chipincludes a pair of input/output terminals that define balancedterminals.
 9. The wireless communication device according to claim 1,wherein the matching circuit includes first and second inductanceelements and first and second capacitance elements.
 10. The wirelesscommunication device according to claim 9, wherein the first and secondinductance elements are electrically connected in parallel with thematching circuit.
 11. The wireless communication device according toclaim 9, wherein the first capacitance element is connected in serieswith the first inductance element to define a series resonant circuit.12. The wireless communication device according to claim 9, wherein thesecond capacitance element is connected in series with the secondinductance element to define a series resonant circuit.
 13. The wirelesscommunication device according to claim 9, wherein the first and secondinductance elements include windings wound in opposite directions so asto define a closed magnetic loop and so as to be magnetically coupled toeach other.
 14. The wireless communication device according to claim 1,wherein the matching circuit and the wireless IC chip are connected toeach other by any of magnetic coupling, capacitive coupling, electricfield coupling, electromagnetic coupling and direct current coupling.15. The wireless communication device according to claim 1, wherein theplane conductor and the conductive object are connected to each other byany of magnetic coupling, capacitive coupling, electric field coupling,electromagnetic coupling and direct current coupling.
 16. The wirelesscommunication device according to claim 1, wherein the wireless IC chipis mounted on the feeding substrate or disposed within the feedsubstrate.
 17. An RFID system comprising: a mounting substrate; and awireless communication device fixed on the mounting substrate; whereinthe wireless communication device includes: a wireless IC chip thatprocesses a high-frequency signal; and a feeding substrate including acoil conductor, a plane conductor, and a matching circuit that isconnected to the wireless IC chip and that has a predetermined resonantfrequency; wherein the coil conductor and the plane conductor areconnected to the matching circuit; and the wireless communication deviceis configured such that when the feeding substrate is arranged to face aconductive object in a planar view, the conductive object overlaps theplane conductor and does not overlap the coil conductor.
 18. The RFIDsystem according to claim 17, wherein the mounting substrate is aprinted circuit board, an article, or a package of an article.